Repeatability of diffusion-weighted MRI of the prostate using whole lesion ADC values, skew and histogram analysis

To investigate the repeatability of diffusion-weighted imaging parameter including ADC-derived histogram values in prostate cancer.

10 patients with prostate cancer were prospectively recruited to a retest cohort. 3 T diffusion-weighted MRI of the prostate was acquired consecutively with patient getting off the scanner between studies. Prostatectomy-histopathology defined tumour regions-of-interest were outlined on ADC maps and diffusion-weighted metrics including histograms were calculated. The coefficient of reproducibility (CoR) and Bland-Altman plots were used to assess repeatability.

10^th centile, 90^th centile, and median ADC showed good repeatability with mean difference ranging from -0.005 to -0.025 × 10³ mm²s^-1, and CoR ranging from 0.271-0.294 × 10³ mm²s^-1 of scan 1 mean). Two measures of heterogeneity and simplified texture, IQR and mean local range, had only moderate repeatability. IQR had a mean difference of -0.032 × 10³ mm²s^-1 between scans with CoR 0.181 × 10³ mm²s^-1 (56% of scan 1 mean). Mean local range had a mean difference -0.008 × 10³ mm²s^-1 between scans (37% of scan 1 mean). Bland-Altman plots showed good repeatability for test and re-test analysis for median, percentile and mean range values. All ADC values had good reliability regardless of whether the tumour border was included in quantitative analysis. ADC histogram skew had poor repeatability, CoR 0.78 × 10³ mm²s^-1 (373% of scan 1 mean).

10^th and 90^th centile ADC demonstrated sufficient repeatability for clinical use. However, more advanced measures of heterogeneity such as histogram skew, IQR, or mean local range may be limited by their repeatability.